Electrodeposition of bright zinc



Patented Aug. 8, 1944 2,355,5n rmcrnonarosrnou 0F amour zmc John Leighton Bray, La Fayette, and Robert Eugene Howard, West Lafayette, Ind., assignors' Purdue Research Foundation, La Fayette,

Ind.. a corporation of Indiana No Drawing. Application October 3, 1941, Serial No. 413,502

1 Claim. (01. 204-55) This invention relates generally to the electrodeposition of zinc, and particularly to a process and materials by means of which bright, continuous deposits of zinc may be obtained electrolytically from acid zinc sulfate solutions.

In the past, most of the methods used in electrogalvanizing resulted in dark or dull plates which had neither eye-appeal nor too great utility as protective coatings because of the coarseness and non-uniformity of the deposit on the plated objects.

Heretofore the electroplating of zinc from sulfate solutions was carried on almost universally at rather low current densities, usually of the order of 20 amperes per square foot. Much higher current densities, approximating 1000 amperes per square foot,'have been employed recently in the electrodeposition of zinc; however,

the commercial designation of about two ounces per square foot was obtained.

The cathodes were cleaned bysubjecting them to an anodic' pickling treatment in a 10% sulfuric acid solution for one minute at a current density of approximately 600 amperes per square foot.

The anodes employed in our experiments were pure lead and had an area of approximately eleven times that of the cathode, thus making the anode current density correspondingly smaller than that of the cathode.

, The variables of temperature, acidity, and concentration of zinc sulfate were kept practically constant It was discovered that predictable results could be obtained when the temperature of the platingsolution was maintained between 14 this work has been directed exclusively to the electro-winning of zinc from its ores.

A primary object of our invention is to provide a method for galvanizing metals to a bright finish by electrolytic means, employing commercially attractive current densities.

Another object of the invention is to provideaddition agents for use in electrogalvanizing processes, which addition agents will effect a bright deposit of zinc over a wide range of current density.

Other and ancillary objects and advantages of our invention will become apparent to those skilled in the art from the following description and explanation of the invention.

We have discovered that bright zinc may be deposited electrolytically, between certain limits of current density, from acid zinc sulfate solutions which contain certain addition agents. In order to acquaint those skilled in the art with the nature of our addition products and the range of current density within which a satisfactory bright zinc deposit may be obtained, we will now set out the findings of our experiments and illustrate our process by several specific examples.

In the procedure followed in our investigations it was found desirable to maintain constant all known variables except the one under consideration. Accordingly, solutions of known concentrations in zinc sulfate, sulfuric acid, and the addition agent were subjected to electrolysis at different current densities. The cathodes.-employed were low-carbon, bright-annealed, steel wires, 0.106 inch in diameter and approximately seven inches long. Four inches of this length were immersed in the plating solution, giving a cathode area of 0.00925 square foot. In order to insure a uniform current density distribution around the periphery of the cathode, provision was made for rotating it at between substantially 15 and revolutions per minute. The test samples were plated until a deposit corresponding to C. and 20 C., the acidity at approximately 0.5 N, and the concentration of zinc sulfate between 20% and 24%. Under these conditions the effect of currentv density and concentration of the addition agents was investigated. The addition agents tried were pyridine and triethylene tetramine.

A series of solutions was prepared in which the concentration of the addition agent varied from 0.005 M to 0.015 M. Each solution was treated electrolytically at a number of current densities and the appearance of the plated object (cathode) observed. The luster characteristic of each sample was classified according to its reflectivity: matte, meaning a dull finish, showing no luster whatever; "semi-metallic referring to the borderline case between matte and metallic luster; metallic referringto a good reflective deposit; and mirror denoting only the most highly reflective deposits. -Whenever the term bright is used in this application to describe the luster characteristic of the zinc deposit, it is intended to include all the degrees of luster covered by the terms semi-metallic, "metallic," and mirror.

Examples of specific embodiments of our invention, in terms of operating data obtained from our experiments, will now be given.

Table I.-0peratino data and observation of samples plated at 0.006 M pyridine Current Av.

. Time of Sam le density, solution num r amperes temp, Color Luster per sq. ft. O.

EE 1.. 600 17 5 Light grey Matte EE 2 400 17 7 do Mirror EE 3--.- 200 15 10 ...d0 Do. EE 4 1'- 10 Dark grey Matte EE 5 15 12 Light grey. Min-or EE 6 800 16 4 ..'d0 Do. .1513 7- 700 17 5 EE 8 600 17 5 EE 9 500 17 v 6 BE 10... 1,000 17 3 EB 11. 300 l6 l0 2 v 2,355,505 Table II.Samples plated at 0.008 M pyridine Table VI.Samples plated at 0.13 M triethylene tetramine Current Av.

Time of 53$ 3; $5338 EEK??? color Lust" 5 1 g q- Time of mm. am 8 6118 y, 50 on Der sq. ft, C 5 Hum amperes tenp" 51in}, Color Luster per sq.it.

EB 1 500 15 5 Light grey- Matte. EB 2--.. 200 16 15 do s emi- 001m" 600 17 5 Dark my? samth me g 200 17 10 Light grey.. Met.

300 16 10 d0.. Semi- 110 18 150 10 150 16 21 250 15 12 do Do. 150 16 10 100 15 15 Dark grey Met. 160 10 150 15 12 .do Do. 200 15 11 Light grey Do. 16 11 300 15 1 do 250 '11 12 400 16 230 11 1a 500 17 200 11 10 1 000 20 300 11 10 11 1 1 600 12 2 Table VII.--Samples plated at 0.15 M trzethylenc EB 13.... 1,000 10 3 t t m Table III.Samples plated at 0.010 M pyridine Current Av Time of Sample density, solution run. Color Luster number amperes tcmp., min Current. Av. Tim f per sq. ft. C. Sam 1e density, solution Color Lust" num er amperes tem 4 1 persq.ft. "CI? GB 1 600 18 5 Dark grey Matte.

GB 200 18 10 -.do Do. E13 500 16 L n 3% 23 3411 191 3 5 i i: re Matte. .000 w EA 9... 220 17 15 do i Semi- GB 100 18 15 Dark grey Met. EDI 600 16 5 d 15 GB 50 15 15 .do Semio.

21 1 do g GB 7 150 14 Lighjt grey 15 Dark Matte GB s.... 180 14 o ED 10 130 15 12 0 GB 0 200 15 ED 11 140 15 11 o Do GB 10. 300 16 ED 12... 150 15 11 Light grey. s e m 1- GB 11. 400 15 ED 13 200 15 m d 1 am GB 12--. 500 11 i m" o n 0 GB 13. 50 17 15 Dark grey Met. GB 14... 500 15 5 Light grey $81111- Table IV.Samples plated at 0.012 -M pyridine GB 15 255 16 10 a5 M11 5 0131511: 200 v15 10 do Mirror Current Av. GB 17-.. 200 16 10 do Do Sam 12 density, solution 0 color Lugter 11 m u or 40 The following conclusions are apparent from ths foregoing data. Bright zinc deposits may be 600 7 5 Light m i obtained from acid zinc sulfate solutions by using 200 17 u metpyridine as an addition agent at concentrations 150 11 10 1111111311111: 13? of 0.006 to 0.010 M and current densities between 1% lfiialilktgreyu Do. 150 and 600 amperes per square foot. Bright zinc 8 8 3 :2} deposits may be obtained from acid zinc sulfate :53 1g 1; fiarktgre grime. solutions by using triethylene tetramine as an gh F addition agent at concentrations of about 0.15 2 3 3 M and current densities between 150 and 600 am- 0 peres per quare fOOiJ.

Having described our invention what we claim The effect of triethylene tetramme as an addiand wish t t t by Letters Patent is: tion agent is shown in the following tables: The process of roducing bright electrode- Table V.Operating data and observation of posited zinc which comprises plating zinc onto 1:.

5 cathode 'at a current density in the range from samples plated at 0.11 M triethylene tetramine 150 to 600 amperes per square foot of cathode Current Av. Tim I surface from a bath at a temperature approxig 12,; 95 & Color Lu mately that of the range 14 to 20 C., said bath per 3. it. 0?" consisting of zinc sulfate, water, sulfuric acid and an addition agent, the bath containing from 20% GA 600 1a 5 1.1 m my Mum to 24% of zinc sulfate, and being approximately 82 150 {3 :8 half-normal in acidity from said sulfuric acid, GA 4:: 100 15 15 1111313111 1331 said addition agent being pyridine and being presi 5"" L111 mil-e ent in the bath in quantity to provide a molar 3,3 concentration in the range from 0.006 to 0.010. I a a 1: 12 1 011 9122:: 1,000 15 3 3131133113 Qfa; JOHN LEIGHTON BRAY. GA 200 20 10 Dark grey Met. ROBERT EUGENE HOWARD. 

